Two‐component Systems in Sensing and Adapting to Acid Stress in Escherichia Coli

Abstract

Two-component signal transduction systems (TCSs), which are used extensively by bacteria, perceive environmental stress and transmit the information via phosphorelay to adjust multiple cellular functions for adaptation. Various TCSs are involved in the acid resistance of bacteria. The EvgS–EvgA system is a TCS that confers acid resistance to Escherichia coli cells. Activation of the sensor EvgS initiates a cascade of transcription factors, EvgA, YdeO, and GadE, which induce the expression of a large group of acid resistance genes. EvgS activation also activates another TCS, the PhoQ–PhoP system, via a small connector protein, SafA. In this chapter, a model of signal transduction cascade proceeding from EvgS–EvgA to PhoQ–PhoP and then to RssB (connected by SafA and IraM), as well as how this cascade contributes to acid resistance, is discussed. Furthermore, we searched for signals activating EvgS and found that a high concentration of alkali metals (Na+ and K+) and low pH were essential for the activation. The periplasmic sensor region of EvgS was necessary for EvgS activation, but the cytoplasmic linker domain, which connects the transmembrane region and the histidine kinase domain, was also required for low-pH perception. These results suggested the complexity of the acid resistance gene regulation involving TCSs and also how the pH message is perceived.